In a portable terminal device such as a portable telephone, a PHS (Personal Handy phone System), or PDA (Personal Data Assistance, Personal Digital Assistants: portable-type information communication equipment for individual persons), the number of support functions tends to increase. Therefore, in order to meet the increasing number of functions, a lithium ion battery realizing a capacity growth and a miniaturization is being developed.
There is a related art of a charging system, for example, disclosed in a patent document 1. The battery charging system disclosed in the above document is such that the ambient temperature of an electrical storage device is sensed, and the full-charging voltage at the time of completion of charging the battery is changed in accordance with the ambient temperature. Further, it is so constructed that, when the voltage of the battery exceeds the full-charging voltage, the charging of the battery is stopped.
Also, a related art of a battery charging system disclosed in a patent document 2 is such that the temperature of the battery is sensed, and an attainment target temperature of the battery is changed in accordance with the sensed temperature, and the charging electric current is changed in accordance with the changed attainment target temperature. This charging system is so constructed that, when the temperature of the battery exceeds the attainment target temperature, the charging of the battery is stopped.    Patent Document 1: Japanese Laid-open Patent Publication No. 2002-58174    Patent Document 2: Japanese Laid-open Patent Publication No. 2001-136675